It is generally recognized that polyurethanes possess excellent toughness (e.g. abrasion resistance, hardness, high tensile strength) and solvent resistance as compared with "rubbery" materials such as styrene-butadiene (SBR), butadiene and even acrylate-type materials. These properties of toughness and solvent resistance make polyurethanes a preferred material for various coating and molding applications. In forming the polyurethane, the polymer is generally dispersed or dissolved in an organic solvent. Unfortunately the use of solvents is becoming increasingly expensive. Also solvent removal may create ecological problems and further contribute to the expense of solvent-based processess.
To overcome the problems associated with solvent-based systems, aqueous polyurethane latices have been developed. Unfortunately for many applications, the toughness and chemical resistance are not provided by these latices to the same extent as with the solvent-based systems. The properties of polyurethane latices, especially in coating applications, more nearly resemble those obtained using conventional "rubbery" type materials such as SBR. Since the cost of the polyurethane latices is also high, the use of conventional latices (SBR and acrylic especially) in many applications has continued.
Presently there is a need to upgrade the properties of the conventional latices to more nearly resemble those of solvent-based polyurethanes. Specifically it would be desirable to provide coatings based on conventional aqueous latex systems which offer improved toughness and solvent resistance while avoiding or reducing the use of organic solvents.